Structures and energetics of small lead cluster ions

By a combination of gas phase ion mobility measurements and relativistic density functional theory calculations with inclusion of spin-orbit coupling, we assign structures of lead cluster cations and anions in the range between 4 and 15 atoms. We find a planar rhombus for the tetramer, a trigonal bipyramid for the pentamer, and a pentagonal bipyramid for the heptamer, independent of charge state. For the hexamer, the cation and anion structures differ: we find an octahedron for the anion while the cation consists of fused tetrahedra. For the octamer, we find in both cases structures based on the pentagonal bipyramid motif plus adatom. For the larger clusters investigated we always find different structures for cations and anions. For example, Pb(12)(-) is confirmed to be a hollow icosahedron while Pb(12)(+) is a truncated filled icosahedron. Pb(13)(+) is a filled icosahedron but Pb(13)(-) is a hollow icosahedron with the additional atom capping a face. In order to get experimental information on the relative stabilities, we investigated the collision induced dissociation mass spectra for the different cluster sizes and charge states, and observe a strong correlation with the calculated fragmentation energies. Up to n = 13 the main fragmentation channel is atom loss; for the larger cluster sizes we observe fission into two large fragments. This channel is dominant for larger anions, less pronounced but clearly present for the cations.     

Structures of tin cluster cations Sn3(+) to Sn15(+)

We employ a combination of ion mobility measurements and an unbiased systematic structure search with density functional theory methods to study structure and energetics of gas phase tin cluster cations, Sn(n)(+), in the range of n = 3-15. For Sn(13)(+) we also carry out trapped ion electron diffraction measurements to ascertain the results obtained by the other procedures. The structures for the smaller systems are most easily described by idealized point group symmetries, although they are all Jahn-Teller distorted: D(3h) (trigonal bipyramid), D(4h) (octahedron), D(5h) (pentagonal bipyramid) for n = 5, 6, and 7. For the larger systems we find capped D(5h) for Sn(8)(+) and Sn(9)(+), D(3h) (tricapped trigonal prism) and D(4d) (bicapped squared antiprism) plus adatoms for n = 10, 11, 14, and 15. A centered icosahedron with a peripheral atom removed is the dominant motif in Sn(12)(+). For Sn(13)(+) the calculations predict a family of virtually isoenergetic isomers, an icosahedron and slightly distorted icosahedra, which are about 0.25 eV below two C(1) structures. The experiments indicate the presence of two structures, one from the I(h) family and a prolate C(1) isomer based on fused deltahedral moieties.     

Gas-phase oxidation of isomeric butenes and small alkanes by vanadium-oxide and -hydroxide cluster cations

Bare vanadium-oxide and -hydroxide cluster cations (V(m)O(n)H(o)+, m = 2-4, n = 1-10, o = 0, 1) were generated by electrospray ionization in order to examine their intrinsic reactivity toward isomeric butenes and small alkanes using mass spectrometric techniques. Two of the major reactions described here concern the activation of C-H bonds of the alkene/alkane substrates resulting in the transfer of two hydrogen atoms and/or attachment of the dehydrogenated hydrocarbon to the cluster cations; these processes are classified as oxidative dehydrogenation (ODH) and dehydrogenation, respectively. For the dehydrogenation of butene, it evolved as a general trend that high-valent clusters prefer ODH resulting in the addition of two hydrogen atoms to the cluster concomitant with elimination of neutral butadiene, whereas low-valent clusters tend to add the diene with parallel loss of molecular hydrogen. Deuterium labeling experiments suggest the operation of a different reaction mechanism for V2O2(+) and V4O10(+) compared to the other cluster cations investigated, and these two cluster cations also are the only ones of the vanadium-oxide ions examined here that are able to dehydrogenate small alkanes. The kinetic isotope effects observed experimentally imply an electron transfer mechanism for the ion-molecule reactions of the alkanes with V4O10(+).     

Copper doping of small gold cluster cations: influence on geometric and electronic structure

The effect of Cu doping on the properties of small gold cluster cations is investigated in a joint experimental and theoretical study. Temperature-dependent Ar tagging of the clusters serves as a structural probe and indicates no significant alteration of the geometry of Au(n) (+) (n = 1-16) upon Cu doping. Experimental cluster-argon bond dissociation energies are derived as a function of cluster size from equilibrium mass spectra and are in the 0.10-0.25 eV range. Near-UV and visible light photodissociation spectroscopy is employed in conjunction with time-dependent density functional theory calculations to study the electronic absorption spectra of Au(4-m)Cu(m) (+) (m = 0, 1, 2) and their Ar complexes in the 2.00-3.30 eV range and to assign their fragmentation pathways. The tetramers Au(4) (+), Au(4) (+)[middle dot]Ar, Au(3)Cu(+), and Au(3)Cu(+)[middle dot]Ar exhibit distinct optical absorption features revealing a pronounced shift of electronic excitations to larger photon energies upon substitution of Au by Cu atoms. The calculated electronic excitation spectra and an analysis of the character of the optical transitions provide detailed insight into the composition-dependent evolution of the electronic structure of the clusters.     

Structures and energetics of helium cluster cations: equilibrium geometries revisited through the genetic algorithm approach

Equilibrium geometries and dissociation energies of He(N)(+) clusters have been calculated for N=3-35 using an extended genetic algorithm approach and a semiempirical model of intracluster interactions [P. J. Knowles, J. N. Murrell, and E. J. Hodge, Mol. Phys. 85, 243 (1995)]. A general aufbau principle is formulated for both ionic cores and neutral solvation shells, and the results are thoroughly compared with other theoretical data available for helium cluster cations in literature.     

Photodissociation of iron oxide cluster cations

Iron oxide cluster cations, Fe(n)O(m)(+), are produced by laser vaporization in a pulsed nozzle cluster source and detected with time-of-flight mass spectrometry. The mass spectrum exhibits a limited number of stoichiometries for each value of n, where m > or = n. The cluster cations are mass selected and photodissociated using the second (532 nm) or third (355 nm) harmonic of a Nd:YAG laser. At either wavelength, multiple photon absorption is required to dissociate these clusters, which is consistent with their expected strong bonding. Cluster dissociation occurs via elimination of molecular oxygen, or by fission processes producing stable cation species. For clusters with n < 6, oxygen elimination proceeds until a terminal stoichiometry of n = m is reached. Clusters with this 1:1 stoichiometry do not eliminate oxygen, but rather undergo fission, producing smaller (FeO)n(+) species. The decomposition of larger clusters produces a variety of product cations, but those with the 1:1 stoichiometry are always the most prominent and these same species are produced repeatedly from different parent ions. These combined results establish that species of the form (FeO)n(+) have the greatest stability throughout these small iron oxide clusters.     

Photodissociation of chromium oxide cluster cations

Chromium oxide cluster cations, Cr(n)O(m)+, are produced by laser vaporization in a pulsed nozzle cluster source and detected with time-of-flight mass spectrometry. The mass spectrum exhibits a limited number of stoichiometries for each value of n, where m > n. The cluster cations are mass selected and photodissociated using the second (532 nm) or third (355 nm) harmonic output of a Nd:YAG laser. At either wavelength, multiphoton absorption is required to dissociate these clusters, which is consistent with their expected strong bonding. Cluster dissociation occurs via elimination of molecular oxygen, or by fission processes producing stable cation species and/or eliminating stable neutrals such as CrO3, Cr(2)O(5), or Cr(4)O(10). Specific cation clusters identified to be stable because they are produced repeatedly in the decomposition of larger clusters include Cr(2)O(4)+, Cr(3)O(6)+, Cr(3)O(7)+, Cr(4)O(9)+, and Cr(4)O(10)+.     

NMR spectroscopy of bismuth fluoride glasses with alkali cations

Results of the ⁷Li, ¹⁹F, and ²³Na NMR studies of ionic mobility in bismuth fluoride glasses in the systems BiF₃-LiF and BiF₃-MF-ZrF₄ (M = Li, Na, K, Cs) are summarized. Analysis of the ⁷Li, ¹⁹F, and ²³Na NMR spectra made it possible to reveal changes in the nature of ion motions in the fluoride, lithium and sodium sublattices of glasses upon temperature variation and to determine their types. The temperature ranges were found where main types of ion motions in the tested glasses are represented by diffusion of lithium ions, reorientations of fluorine-containing groups constituting the glass network, and diffusion of fluorine ions. The role of alkali cations in the formation of ionic mobility in bismuth fluorozirconate glasses is considered.     

Vibrational spectra of small silicon monoxide cluster cations measured by infrared multiple photon dissociation spectroscopy

The first gas-phase infrared spectra of silicon monoxide cations (SiO)(n)(+), n = 3-5, using multiple photon dissociation in the 550-1250 cm(-1) frequency range, are reported. All clusters studied here fragment via loss of a neutral SiO unit. The experimental spectra are compared to simulated linear absorption spectra from calculated low energy isomers for each cluster. This analysis indicates that a "ring" isomer is the primary contributor to the (SiO)(3)(+) spectrum, that the (SiO)(4)(+) spectrum results from two close-lying bicyclic ring isomers, and that the (SiO)(5)(+) spectrum is from a bicyclic ring with a central, fourfold-coordinated Si atom. Experiment and theory indicate that the energies and energetic orderings of (SiO)(n)(+) isomers differ from those for neutral (SiO)(n) clusters.     

Ab initio calculations on bismuth cluster polycations

Ab initio calculations on bismuth polycationic species of the types Bi(n(n-2))+, Bi(n(n-4))+, and Bi(n(n-6))+ (n = 3 - 12) were performed at the Hartree-Fock and density functional theory levels in order to investigate their general properties and the applicability of Wade's rules on bismuth polycations. Some exceptions to Wade's rules were encountered, and, moreover, several predicted and calculated minima show only meta-stable behavior. The bonding in bismuth polycations is characterized by a high degree of electron delocalization and "three-dimensional aromaticity".     

Photodissociation of cobalt and nickel oxide cluster cations

Cobalt and nickel oxide cluster cations, Co(x)O(y)(+) and Ni(x)O(y)(+), are produced by laser vaporization of metal rods in a pulsed nozzle cluster source and detected using time-of-flight mass spectrometry. The mass spectra show prominent stoichiometries of x = y for Co(x)O(y)(+) along with x = y and x = y - 1 for Ni(x)O(y)(+). The cluster cations are mass selected and multiphoton photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Although various channels are observed, photofragmentation exhibits two main forms of dissociation processes in each system. Co(x)O(y)(+) dissociates preferentially through the loss of O(2) and the formation of cobalt oxide clusters with a 1:1 stoichiometry. The Co(4)O(4)(+) cluster seems to be particularly stable. Ni(x)O(y)(+) fragments reveal a similar loss of O(2), although they are found to favor metal-rich fragments with stoichiometries of Ni(x)O(x-1). The Ni(2)O(+) fragment is produced from many parent ions. The patterns in fragmentation here are not nearly as strong as those seen for early or mid-period transition-metal oxides studied previously.     

Experimental vibrational spectra of gas-phase tantalum cluster cations

We present gas-phase infrared spectra of tantalum cluster cations containing 6-20 atoms. Infrared multiple photon dissociation of their complexes with argon atoms is used to obtain vibrational spectra in the region between 90 and 305 cm(-1). Many spectra have features in common with the vibrational spectra of the lighter homologs, vanadium and niobium, pointing to a common cluster growth mechanism.     

Photodissociation of yttrium and lanthanum oxide cluster cations

Transition metal oxide cations of the form M n O m (+) (M = Y, La) are produced by laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. Cluster oxides for each value of n form only a limited number of stoichiometries; MO(M2O3)x(+) species are particularly intense. Cluster cations are mass selected and photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Multiphoton excitation is required to dissociate these clusters because of their strong bonding. Yttrium and lanthanum oxides exhibit different dissociation channels, but some common trends can be identified. Larger clusters for both metals undergo fission to make certain stable cation clusters, especially MO(M2O3) x (+) species. Specific cations are identified to be especially stable because of their repeated production in the decomposition of larger clusters. These include M3O4(+), M5O7(+), M7O10(+), and M9O13(+), along with Y6O8(+). Density functional theory calculations were performed to investigate the relative stabilities and structures of these systems.     

Formation of gold cluster cations by direct laser vaporization

Gold cluster cations, Au⁺_n, with n= 1 to 6 have been produced by direct laser vaporization of gold metal in a Fourier transform ion cyclotron resonance mass spectrometer. Wavelength studies at λ = 532, 355, and 266 nm show similar results. However, the intensities and intensity ratios of the cluster ions strongly depended on laser power at the two longer wavelengths. Ionization energies of Au⁺ , Au⁺₂, and Au⁺₃ have also been estimated.     

Evidence of liquid state for small bismuth particles

Small bismuth particles have been formed on amorphous carbon films by molecular beam deposition. The pressure during the deposition was less than 1 × 10^?4 Pa. At low thicknesses (<1.5 nm) most of Bi particles are small (2 to 10 nm) and isolated. Electron diffraction and dark field transmission electron microscopy observations (dark field T.E.M.) show that these particles are not crystallized. Increasing the thickness of the deposit, the diameter of aggregates and also the number of crystallized particles increase. Then there is coexistence between non-crystallized and crystallized particles. At thicknesses higher than 2 nm, electron diffractions show rings (indicating the crystallization of particles) which can be indexed in the normal rhombohedral structure of bismuth. In situ low temperature T.E.M. observations of low (or intermediate) thickness Bi deposits performed using a cooling stage show the crystallization of particles. Returning at room temperature, many particles which were not crystallized at the begining of the experiment retain the crystallized structure. It is then necessary to warm up the sample to melt these particles which crystallize again at room temperature. This behaviour agrees with a liquid state for particles after deposition which can be explained by a supercooling phenomenon.     

Activation of the C-I and C-OH bonds of 2-iodoethanol by gas phase silver cluster cations yields subvalent silver-iodide and -hydroxide cluster cations

The gas phase ion-molecule reactions of silver cluster cations (Ag(n)(+)) and silver hydride cluster cations (Ag(m)H(+)) with 2-iodoethanol have been examined using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. These clusters exhibit size selective reactivity: Ag(2)H(+), Ag(3)(+), and Ag(4)H(+) undergo sequential ligand addition only, while Ag(5)(+) and Ag(6)H(+) also promote both C-I and C-OH bond activation of 2-iodoethanol. Collision induced dissociation (CID) of Ag(5)HIO(+), the product of C-I and C-OH bond activation by Ag(5)(+), yielded Ag(4)OH(+), Ag(4)I(+) and Ag(3)(+), consistent with a structure containing AgI and AgOH moieties. Ag(6)H(+) promotes both C-I and C-OH bond activation of 2-iodoethanol to yield the metathesis product Ag(6)I(+) as well as Ag(6)H(2)IO(+). The metathesis product Ag(6)I(+) also promotes C-I and C-OH bond activation.DFT calculations were carried out to gain insights into the reaction of Ag(5)(+) with ICH(2)CH(2)OH by calculating possible structures and their energies for the following species: (i) initial adducts of Ag(5)(+) and ICH(2)CH(2)OH, (ii) the subsequent Ag(5)HIO(+) product, (iii) CID products of Ag(5)HIO(+). Potential adducts were probed by allowing ICH(2)CH(2)OH to bind in different ways (monodentate through I, monodentate through OH, bidentate) at different sites for two isomers of Ag(5)(+): the global minimum "bowtie" structure, 1, and the higher energy trigonal bipyramidal isomer, 2. The following structural trends emerged: (i) ICH(2)CH(2)OH binds in a monodentate fashion to the silver core with little distortion, (ii) ICH(2)CH(2)OH binds to 1 in a bidentate fashion with some distortion to the silver core, and (iii) ICH(2)CH(2)OH binds to 2 and results in a significant distortion or rearrangement of the silver core. The DFT calculated minimum energy structure of Ag(5)HIO(+) consists of an OH ligated to the face of a distorted trigonal bipyramid with I located at a vertex, while those for both Ag(4)X(+) (X = OH, I) involve AgX bound to a Ag(3)(+) core. The calculations also predict the following: (i) the ion-molecule reaction of Ag(5)(+) and ICH(2)CH(2)OH to yield Ag(5)HIO(+) is exothermic by 34.3 kcal mol(-1), consistent with the fact that this reaction readily occurs under the near thermal experimental conditions, (ii) the lowest energy products for fragmentation of Ag(5)HIO(+) arise from loss of AgI, consistent with this being the major pathway in the CID experiments.     

Structures of medium sized tin cluster anions

The structures of medium sized tin cluster anions Sn(n)(-) (n = 16-29) were determined by a combination of density functional theory, trapped ion electron diffraction and collision induced dissociation (CID). Mostly prolate structures were found with a structural motif based on only three repeatedly appearing subunit clusters, the Sn(7) pentagonal bipyramid, the Sn(9) tricapped trigonal prism and the Sn(10) bicapped tetragonal antiprism. Sn(16)(-) and Sn(17)(-) are composed of two face connected subunits. In Sn(18)(-)-Sn(20)(-) the subunits form cluster dimers. For Sn(21)(-)-Sn(23)(-) additional tin atoms are inserted between the building blocks. Sn(24)(-) and Sn(25)(-) are composed of a Sn(9) or Sn(10) connected to a Sn(15) subunit, which closely resembles the ground state of Sn(15)(-). Finally, in the larger clusters Sn(26)(-)-Sn(29)(-) additional bridging atoms again connect the building blocks. The CID experiments reveal fission as the main fragmentation channel for all investigated cluster sizes. This rather unexpected "pearl-chain" cluster growth mode is rationalized by the extraordinary stability of the building blocks.     

Structures of dibromodicyanoaurate complexes with methoxymethyltriphenylphosphonium and tetraphenylstibonium cations

Russian Chemical Bulletin - The reaction of potassium dibromodicyanoaurate with methoxymethyltriphenylphosphonium and tetraphenylstibonium chlorides in water followed by recrystallization from...     

Reactions of indium phosphide cluster cations with ammonia and trimethylamine

Chemistry of indium phosphide clusters is studied using the powerful trapped ion cell techniques of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in conjunction with an external cluster source and ion guide. The external source is capable of generating a wide range of cluster ions which the ion guide loads with high efficiency into the FTICR cell. The differential pumping of the ion guide allows for operation of the FTICR at requisite low pressure conditions while extracting clusters generated in a high pressure environment. Highly selective reactions of indium phosphide clusters are observed with ammonia and trimethylamine. Of all the In_xP⁺_y cluster sizes and stoichiometries studied, only the indium dimer ion reacts exothermically with ammonia. Thermalized In⁺₂ reacts by indium ion transfer to ammonia. Owing to its much higher basicity, trimethylamine is much more reactive. The smaller indium phosphide clusters react by indium ion transfer to trimethylamine. As the clusters become larger, however, the reaction probability decreases to zero.